Aneesh Manohar

Chiral quarks and the non-relativistic quark model☆

Abstract We study some of the consequences of an effective lagrangian for quarks, gluons and goldstone bosons in the region between the chiral symmetry breaking and confinement scales. This provides an understanding of many of the successes of the non-relativistic quark model. It also suggests a resolution to the puzzle of the hyperon non-leptonic decays.

The g1 problem : deep inelastic electron scattering and the spin of the proton

Abstract A recent measurement of the spin-dependent structure function of the proton, g 1 p ( x , Q 2 ), suggest that the quarks spin accounts for little of the protons spin. We analyze several theoretical issues bearing on this result. We discuss the result expected in a variety of quark models. We examine the proposal that gluons contribute to the protons spin in an amount calculable (in terms of gluon distribution functions) in perturbative QCD. We examine the conserved currents associated with Lorentz transformations in QCD, derive sum rules and show that the anomalous (gluonic) U (1) A current, K μ , is not in general to be identified with the gluon spin. Finally, we discuss the ensemble of nucleon matrix elements of quark bilinear operators and urge an experimental and theoretical program to study them.

Strange matrix elements in the proton from neutral-current experiments

Recent results from EMC suggest a nonzero value for 〈p|-ssγμγ5s|p〉; measurements of the pion-nucleon sigma term suggest a large value for 〈p|ss|p〉. In this paper we discuss how elastic neutral-current scattering experiments may be used to extract more information about the “strangeness” of the proton. In particular, one can measure the form factor F2 for 〈p|ss|p〉, as well as the G1 form factor for 〈p|sγμγ5s|p〉. We also show how nonzero strange matrix elements in the proton can be reconciled with the successes of the nonrelativistic quark model.

Equivalence of the chiral soliton and quark models in large N

We prove that the group theoretic structure of the chiral soliton model is identical to that of the naive quark model in the large-NC limit. This implies that all group theoretic calculations such as the FD ratios, gπNNgπNΔ, etc. are identical in the soliton and quark models in large N. This result is true for an arbitrary number of flavors. We also compare the two models for finite NC.

The Evaporation of

Abstract In extended electroweak models with scalar fields carrying lepton number, it is possible for these fields to form extended objects of the Q -ball sort. In general, these are destabilised by the Yukawa coupling of the scalar to neutrinos. This decay process takes place only on the surface of the object, not in the interior. Thus the Q -balls evaporate away. We set up the general theory of this process, find an absolute upper bound for the evaporation rate, and explicitly compute the rate in a simple case.

Q

Abstract Deep inelastic scattering from a polarized spin-one target yields qualitatively new information which is not available in the spin-half case. Among several new structure functions, one, b 1 ( x ), is leading twist in QCD. It can be measured with an unpolarized beam. b 1 ( x ) is small and calculable for a weakly bound collection of nucleons, and therefore its measurement would provide a clear signature for exotic components in a spin-one nucleus.

Balls

Abstract In general, gauge invariance does not require that the two U(1)s in a U(1) × U(1) gauge theory be orthogonal. We examine this possibility in the context of an electroweak SU(2)L × U(1)R × U(1)(B−L)/2 gauge theory. It is shown that the neutral-current experiments determining Hneutral do not restrict this “mixing”. In particular, there could be a second Z in the range 70–110 GeV whose couplings to quarks and leptons are comparable (≈ 1 2 as big ) as those of the Z with a mass of 95 GeV. Measurements of Z production rates or the demand that the theory be grand unifiable could restrict this mixing of U(1)s.

Novel effects in deep inelastic scattering from spin-one hadrons

Abstract We reexamine the bounds on a very light Higgs boson (φ) coming from limits on the decays K→ π + φ and B→ φ +X. We show that, if there are only three families, m φ >2 m τ , and that regardless of the number of families M φ >360 MeV.

TWO Z's OR NOT TWO Z's?

Abstract We analyze inclusive inelastic lepton scattering from polarized targets of arbitrary spin, J . We express the cross-section and lepton spin asymmetry in terms of Lorentz invariant structure functions. In the Bjorken limit all information about the target is summarized by a set of 2 J + 1 quark distribution functions (for each flavor of quark and antiquark) which evolve logarithmically with Q 2 in a manner prescribed by QCD. We present both parton model and operator product expansion analyses. For nuclear targets we present the predictions for these structure functions based on a convolution model in which nuclei are composed only of bound protons and neutrons. Specific examples are worked out in detail.

Limits on a light Higgs boson

Abstract The supernova explosion observed recently in the Large Magellanic Cloud can be used to place the limit σ −35 cm 2 on the neutrino-neutrino scattering cross section. This limit does not depend on any of the details of the theory of supernovae. If v-v scattering is due to the exchange of a scalar particle with mass smaller than the neutrino temperature T v , then the limit on the scalar-neutrino coupling constant is g cc 2 −6 ( T V /10 MeV).